- How well can you manage yourself? If, as an individual contributor, you can't manage yourself, I wouldn't expect you to be good at managing others. For example... Do you take responsibility for your work or blame someone else for every problem? Do you take the initiative, or only do things when you're told to do them? Are you good at solving problems yourself, but also capable of reaching out to others when you need help? Can you provide a reasonable estimate on how long it would take to get something done? Are you good at managing your time and do you meet deadlines? If I delegate a task to you, can I trust you to get it done and to inform me if things are not going according to plan?
- Communication: Can you communicate effectively with your manager and your peers on technical and business issues? If not, I wouldn't expect you to be good at communicating with people who report to you. Can you communicate effectively with less-technical people like product managers and designers?
- Leadership potential: Have you done things like mentoring junior employees or proactively fixing some technical issue that needed to be fixed? Do you look for better ways of doing things? Have you voluntarily taken on increased responsibilities?
- Interpersonal skills: Can you get along with people, especially those whose personal characteristics are different from your own? Would I be able to bring you with me to a meeting with upper management without risking embarrassment (e.g., would you be playing with your phone while the CEO is talking)? Can I trust you to behave legally and ethically (e.g., not sexually harass other employees, have sexual relationships with your subordinates, discriminate based on race or gender or engage in bullying behavior)?
- Technical competence: Are you a good enough programmer that the programmers who you'd supervise could respect you and learn things from you? You wouldn't have to know more than everyone else on your team, but your reason for wanting to manage programmers shouldn't be that you can't cope with programming yourself.
(Disclosure: I've been a manager and have promoted others to management roles with varying degrees of success.)
My short answer is that it's moderately difficult. You might need to give up on programming to focus on aspects like People and Schedule management, Negotiations, Connections etc. At the end of the day, Management is about organizing stuff, be it people, time, resources or life.